Hepatocyte growth factor (HGF) is a unique growth factor, which is unrelated to other well-known polypeptide mitogens. It is a protein expressed in the mesenchymal cells such as lung macrophages and fibroblasts, Kupffer cells in the liver and leukocytes. HGF is secreted in response to cell damage and appears to be important for the regeneration of certain organs and healing of wounds. It is a heterodimer, having disulphide bonded heavy and light chains of approximately 60 and 30 kDa respectively, first synthesized as an inactive precursor. The precursor is cleaved to an active protein in the damaged organ by a specific activator. HGF acts paracrinally, i.e. it affects adjacent cells, as well as endocrinally, i.e. it has a long-distance. The target cells of HGF are fully developed epithelial cells. HGF is produced and is present in high concentrations at sites of organ damage.
The systemic and local production of HGF in various infectious diseases has been studied and high serum HGF concentrations have been observed during acute infectious diseases such as gastroenteritis, sepsis, pneumonia, skin and soft tissue infections and pyelonephritis. Simultaneous with enhanced systemic production of HGF, high HGF concentrations have been found in cerebrospinal fluid during meningitis. Raised HGF concentrations in exhaled breath condensate in patients with pneumonia, which had no correlation to serum levels of HGF, indicated a local production of HGF during pneumonia. Furthermore the stability of HGF in serum has been studied and HGF was found to be very stable in diluted feces samples and several freeze-thaw cycles, different buffers or several years of storage at −20° C. did not affect feces HGF concentrations significantly. High amounts of HGF in feces during diarrhea have been shown to possibly indicate that patient suffers from a transmittable gastroenteritis. Further, monitoring of HGF levels before and after treatment during infectious diseases has been shown to possibly reveal therapeutic failure at an early stage.
Recognizing the clinical importance and differences between recommended therapies, differential diagnosis between inflammatory disorders in the body has been the subject of several investigations. One major clinical problem is determining whether infection or other inflammatory disorders cause the disease. There are several markers that typically are used by physician to establish the right diagnosis such as microscopic analysis and culture of body fluids, white blood cell count, C-reactive protein, plasma procalcitonin and lactate. However, there are still no golden standards to be used. Problems in establishing correct diagnosis occurs daily while treating inflammatory disorders in bowel, ulcers, joint diseases, CNS disorders, peritoneal, pleural and pericardial effusions, among others. The amounts of routine markers such as CRP and WBC might be high in several disorders and cultures are not always positive in spite of an infection. High amounts of HGF and its application in diagnosis and prognosis of infectious diseases are discussed in PCT application PCT/SE2001/001831. Yet in these studies, the whole amount of HGF in the body fluids was determined by ELISA method. Various studies about HGF have been reported. Some studies have used determination of HGF in plasma/serum and urine for diagnosis and screening of diseases such as acute renal deficiency, myocardial infarction, carcinoma of bladder, acute pancreatitis and acute and chronic lung diseases. For this reason, previously described methods such as ELISA and Western blotting have been used. Detection of high amounts of cytokines during inflammatory diseases is not a unique finding. However, in some cases, determination of HGF has been found to be a sensitive method that could detect specific clinical problems much easier than the routine methods (PCT application PCT/SE2001/001831).
The previous described methods such as ELISA and Western blotting are based on an interaction between HGF in the samples and an antibody that binds specifically to HGF. In ELISA, the amount of HGF single-chain and double-chain is determined. By Western-blotting the quality of HGF in the body fluid is determined by detection of apparent molecular masses present in the sample. However the methods are cumbersome and laborious.
The innovative use of biosensors is useful, inexpensive and rapid in this area of analysis. Surface plasmon resonance (BIACORE®) method can be used for the detection of HGF in feces (WO2005/031365). The technique is able to detect HGF levels and quality in a single run.
In the case of infection: In different organs, the levels of HGF are increased locally at the site of infection. The whole amount of protein might be detected by ELISA. Using Biacore® technology, detection of the level of interaction (signals) to monoclonal, polyclonal antibodies to HGF as well as heparan sulphate proteoglycan (HSPG) immobilized to the chip, is high and it correlates positively to the results obtained by ELISA.
In the case of chronic inflammation: In spite of high amounts of HGF in samples that might be found by ELISA, non-significant correlation between ELISA and the results obtained by Biacore® is observed. It might be no or very low signals detected by Biacore® that shows a weak interaction to the ligands. The interaction to c-met protooncogene receptor might be high and the signals correlate positively to the level of immobilization. There is low signal rate at the HSPG channel. Adding HSPG or dextran sulphate to the samples at least 10 minutes prior to analysis might not diminish the signal at the HSPG channel. The protein might be biologically inactive.
The growth factors and cytokines such as Hepatocyte growth factor produced during injuries are released endocrinally and produced locally by the neighbor mesenchymal cells. The protein interacts with the high affinity cell binding specific receptor and sends signal into the cell resulting in regeneration of injured organ. In the case of HGF a non-specific receptor on the cell membrane and extracellular matrix (ECM) is needed to capture the cytokine and make it available to the specific receptor (c-Met receptor). Therefore the variants of HGF which show no affinity to HSPG or other proteoaminoglycans are not captured by ECM after release and might not interact with the specific receptor. Thus the protein might act as inactive in spite of high affinity to c-Met receptor.
In our previous works we have studied HGF by SDS-page, Western blot, ELISA and SPR and shown that the HGF protein (endogenous or recombinant) which did not bind to proteoaminoglycan (HSPG, heparan sulphate) or dextran sulphate, had no biological effect in the in-vivo (hair growth mice) or in-vitro biological activity methods (CCL-53.1 cells) used in our group. We have seen differences in patients with acute infection compared to chronic inflammation in binding affinity to HSPG in SPR method. Our primary conclusion is that in patients with chronic inflammation the high hierarchy cytokines such as HGF are inactivated and therefore they might need exogenous biologically active HGF to stimulate regeneration. As an example treatment with exogenic HGF has been shown to be beneficial in treatment of some cases of chronic leg ulcers (PCT application PCT/SE2001/001831). HGF has been found to enhance migration of healthy neighbor skin epithelial cells towards the damaged area by changing the cytoskletal structure of cells in vitro. An enhanced expression of met proto-oncogene receptor (c-met) in the ulcer area of patients with chronic ulcers is seen. Treatment with exogenous HGF decreased c-met expression significantly. There was a negative correlation between biologically active endogenous HGF concentration in the ulcer secrete and met proto-oncogene receptor (c-met) expression. Treatments with exogenous HGF in the patients with a low amount of endogenous HGF and high met proto-oncogene receptor (c-met) expression caused vascular proliferation and ulcer area reduction. This model of organ injury in the skin and the related events might be true in other organ tissues as well.